(1) Field of the Invention
The present invention relates to display devices, and particularly to a display device using current-driven luminescence elements.
(2) Description of the Related Art
Display devices using organic electroluminescence (EL) elements are well-known as display devices using current-driven luminescence elements. An organic EL display device using such self-luminous organic EL elements does not require backlights necessary in a liquid crystal display device and is most suitable for increasing device thinness. Furthermore, since viewing angle of such an organic EL display is not limited, practical application as a next-generation display device is expected. Furthermore, the organic EL elements used in the organic EL display device are different from liquid crystal cells, which are controlled according to voltage applied thereto, in that the luminance of the respective luminescence elements is controlled according to the amount of current flowing thereto.
In the organic EL display device, the organic EL elements included in the pixels are normally arranged in rows and columns. An organic EL display is called a passive-matrix organic EL display, in which organic EL elements are provided at crosspoints of row electrodes (scanning lines) and column electrodes (data lines) and voltages corresponding to data signals are applied between selected row electrodes and the column electrodes to drive the organic EL elements.
On the other hand, in an organic EL display device referred to as an active-matrix organic EL display device, a switching thin film transistor (TFT) is provided in each crosspoint between scanning lines and data lines, the gate of a drive element is connected to the switching TFT, the switching TFT is turned ON through a selected scanning line so as to input a data signal from a signal line to the drive element, and the organic EL elements are driven by the drive element.
Unlike in the passive-matrix organic EL display device in which, only during the period when each of the row electrodes (scanning lines) is selected, does the organic EL element connected to the selected row electrode generate photons, in the active-matrix organic EL display device, it is possible to cause the organic EL element to generate photons until a subsequent scan (selection), and thus increase in the number of scanning lines does not cause reduction in display luminance. Therefore, the active-matrix organic EL display device can be driven at a low voltage and thus allows for reduced power consumption.
For example, International Publication No. 2010/041426 (Patent Reference 1) discloses a circuit configuration of a pixel unit in an active-matrix organic EL display device and a method of driving the display device.